1. Field of the Invention
The present invention relates to a microorganism which is used to produce L-glutamic acid by fermentation, and a process for producing L-glutamic acid by fermentation using the microorganism. L-glutamic acid is an amino acid which is important as a seasoning and an ingredient in medicines.
2. Description of the Related Art
L-glutamic acid has been produced thus far by fermentation using mainly so-called glutamic acid-producing microorganisms belonging to the genus Brevibacterium, Corynebacterium or Microbacterium or their mutants (Amino-Acid Fermentation, Gakkai Shuppan Center, pp. 195-215, 1986). With respect to a process for producing L-glutamic acid using other strains, a process using microorganisms belonging to the genus Bacillus, Streptomyces, Penicillium or the like (U.S. Pat. No. 3,220,929) and a process using microorganisms belonging to the genus Pseudomonas, Arthrobacter, Serratia, Candida or the like are known (U.S. Pat. No. 356,387). Production levels of L-glutamic acid have been increased considerably by conventional methods. However, to meet the increasing demand in the future, the development of a process for producing L-glutamic acid more efficiently at lower costs has been desired.
Since Escherichia coli has a high growth rate and the genetic analysis thereof has progressed remarkably, there is a possibility that this microorganism may be used as an excellent L-glutamic acid-producing microorganism in the future. However, according to a previous report, the amount of L-glutamic acid accumulated by Escherichia coli was as low as 2.3 g/liter (J. Biochem., vol. 50, pp. 164-165, 1961). Nevertheless, it has been recently reported that a mutant which is deficient in or has decreased levels of .alpha.-ketoglutaric acid dehydrogenase (hereinafter referred to at times as ".alpha.-KGDH") activity produces high levels of glutamic acid (French Patent Laid-Open No. 2,680,178).